Australia's Science Forum

Hi everyone,
I really need to know if anyone has had issues with test tubes either spitting water (big time - I mean nearly the entire contents coming out like a projectile) instead of boiling, or even just exploding (glass shattered and spread in about a 2m radius). We have just bought new test tubes and the only thing I can think of is that because they don't have any scratches or anything the water is getting super-heated or something.
We have cancelled all test tube heating pracs (not doing much for the confidence of the year 7 kids - this is their introduction to bunsens!!). Great way to explain how lab coats and safety glasses are so important though!!
Thanks for any feedback
Rosalie

Oh, yes, it happens.

You should always use boiling chips to prevent flash boiling.

It's what they're for.

Thanks Graham, We have never had this happen before so that's why we are concerned. Boiling chips is our next step although we have never needed to use them in previous years. We have hardly any boiling chips left and I have been unable to find a supplier. We certainly don't have enough to go around a full year 7 class. I we only use them in 1 or 2 senior chem pracs usually and I rescue as many as I can from going down the sink each time but our supply has diminished significantly. Anyone know where I can get more?

we have not used boiling chips in T/tubes, but sounds like a good idea. I smash broken crucibles and use the porcelain chips for boiling chips. Unlimited supply, ha ha
Lada

Thanks Lada, I have tried to smash crucibles (especially the abundant supply of lids!) but I have not managed to get the pieces small like the boiling chips and I usually make more mess than I care to clean up... How do you go about it? Obviously my method of a hammer and a zip lock bag isn't good enough because the bag always breaks. I can't remember what else I tried before I gave up.

The same method as you, but I wrap the ziplock in hand towel. Seems to protect the plastic bag but still smashes the lids. I do one or two at the time.
Lada

Small pieces of broken glass will also do in a pinch. (Lumps rather than shards.)

Who did you buy the test tube from are they new ones as it may be a problem with the supplier as some suppliers bring them in from China and they are not up to our standards.

I can't remember, I will have to look through our invoices. Thanks for ideas everyone

Hi Rosalie
I have just purchased marble chips from Serrata Item No 1038843. Its under Calcium Carbonate with Marble chips in brackets.
I have not had to buy test tubes since there was plentiful supply in store room when I arrived here 9 years ago. Hope I dont get the exploding type when I eventually do have to buy more
judy

Hi

You using the Boiling Tubes for boiling (as opposed to the medium sized test tubes)?

I only allow any boiling or heating in the larger size tubes- the med ones spit

A few years ago, we had a memo on poor test tubes, being sold at _________________. We have seen purchased heating t-t for of course Heating. And kept the other ones for mixing only. Teacher needs to ask for heating or Non heating. When you read in some of the booklets, Australian Standard for mixing, in tiny little print. Just another way to get us.

Judy- boiling chips are not the same as calcium carbonate chips.

Dont use calcium carbonate or marble chips , as boiling chips!

That's what I've always used.
J

Ocean Breeze wrote:Judy- boiling chips are not the same as calcium carbonate chips.

Dont use calcium carbonate or marble chips , as boiling chips!

Well, it depends. Actual "boiling chips" are often made of calcium carbonate but with a teflon coating to ensure that they are even more chemically inert.

If they're just being used in the water bath, or for a boiling demonstration, you can get away with using raw calcium carbonate. Just be sure to keep used chips seperate from clean stock and watch for discoloration.

Ideally though, boiling chips are porous, and thus will retain chemicals in solution, so really should not be reused at all.

Did a quick search on boiling chips. They come in different types. Black silicon carbide chips (carborundum), porous carbon chips and calcium carbonate boiling chips (called Boileezers from Fisher Scientific not to be used with conc H2SO4 or strong alkalis). I use glass beads which are 6mm in diameter.

As for exploding test tubes, we had a batch of these years ago where the bottoms kept blowing off. If I remember rightly they were government stores issue. Haven't had any problems since going with supplies from Omega scientific and if there are problems they are sorted pretty quickly. Another thought is that your test tubes might be culture tubes which are thin walled and are not to be used for heating anything. I have some boxes of culture tubes but I have written profusely across all the surfaces of the boxes that they are not for heating.

Lyn.

P.S. The contents of any test tube will have a tendency to eject violently if the students hold the test tube stationary in the flame instead of moving it gently back and forth through the flame to heat the contents.

Thanks for all your ideas, guys. The boiling chips we've had in the past are "anti-bumping granules' which is what I have been looking for as replacements. Perhaps I should broaden my search. We will use the crushed crucible lids until I find an alternative. I am quite sure they are heating test tubes. I thought the teacher was watching the one that 'exploded' but it turns out they were with the next group so it is possible that when the water 'shot out' of the test tube they got a fright and smashed it on the bunsen. Just a possible scenario... although I don't know if that scenario explains the distance the glass shards managed to get to.

We use porcelein chips too - for distillation etc - would not use marble chips.
Until I had risk assess I was not always aware of what teachers were doing with the items they asked for. Silly me. I just thought you were talking about marble chips and wondered why you couln't find them.
Judy

A couple of years ago I purchased test tubes from Livingstone that had a thicker wall. These are terrific and have survived much abuse without exploding. The thicker glass wall is the answer I'm sure.
Cheers
Mother